Two inherited dental conditions, dentinogenesis imperfecta (DGI) and juvenile periodontitis (JP) are co-segregating in five generations of a large inbred Southern Maryland kindred. Previous studies have documented that DGI is inherited as an autosomal dominant trait, while JP demonstrates either an autosomal recessive or X-linked dominant mode of inheritance. However, the appearance of only a single recombinant mode of inheritance. However, the appearance of only a single recombinant individual among the 47 members of this family suggests that the JP observed in this kindred may also be due to an autosomal dominant gene. The gene determining Gc phenotypes has been assigned to human chromosome No. 4 and has demonstrated close linkage with the locus for DGI. Therefore, by inference, the preliminary analysis of data from a segment this family suggest that JP is also on chromosome 4. Two additional markers for chromosome No. 4, i. e., the gene for plasminogen and the quinacrine fluorescent polymorphism at the centromere, will also be utilized in this study. Genotypic data for these markers on all individuals in this kindred will be analyzed to determine linkage relationships among the five loci. Moreover, such information may also permit more exact ordering of the linear sequence of these genes in the centromeric region of chromosome No. 4.